During a semiconductor package assembly process, there may be a need to detach a semiconductor chip from an adhesive tape carrier in chip bonding or flip chip bonding processes. This detachment is usually necessary where a slice of wafer comprising a plurality of said semiconductor chips has been mounted onto an adhesive tape (such as Mylar Film) for dicing, and each diced chip has to be removed from the adhesive tape and placed at a bonding location.
The first step of the detachment process generally includes generating a delamination or peeling action between the semiconductor chip and the adhesive tape. This is induced by an upward force exerted by a push-up tool located underneath the chip and adhesive tape, which is reinforced by suction force from a vacuum platform holding down the adhesive tape. It is usually necessary to sufficiently delaminate the chip from the adhesive surface of the tape before total removal therefrom. That is to enhance the ability to separate the chip from the adhesive tape, and also to avoid damage to the chip. Especially for chips that are thinner and larger, the adhesion between surfaces may cause a bending moment or stress in the chip. If this is too large, the chip will crack or break.
There are various apparatus in the prior art that seek to promote delamination between the chip and adhesive tape. They commonly comprise a holder securing the adhesive tape and motorized linear actuators installed underneath the holder and adhesive tape to control a detachment or push-up tool. The most common technique to detach a semiconductor chip or device from an adhesive tape uses single or multiple push-up pin(s) as push-up tools to lift the chip up above a platform while the platform is holding the tape down by vacuum suction, such as in U.S. Pat. No. 5,755,373 entitled “Die Push-Up Device”. This push-up action of the pin(s) will create a force to peel the chip away from the adhesive tape. For this technique, the driving mechanism consists of a motorized linear actuator installed underneath the said vacuum platform (see FIG. 2 of the patent). The push-up pins are driven by this linear actuator to move vertical upwards and downwards. Alternative designs have also been implemented for peeling the chip from the adhesive tape, such as U.S. Pat. No. 4,990,051 entitled “Pre-peel Die Ejector Apparatus”, which teaches having two or more steps comprised of outer and inner housing sections to control the deformation of the tape to improve the effectiveness of said push-up pin(s).
The disadvantage of using push-up pins is that a strong bending moment will be induced by the push-up action on the semiconductor chip if the induced force is not large enough to peel the chip off from adhesive tape. The bottom surface of chip will experience high compressive stress at the location(s) where the push-up pin(s) are directly acting upon the chip. The top surface of the die located directly above the push-up pin(s) will experience very high tension as the chip bends. The chip will be susceptible to crack failure if the strain induced by this bending moment exceeds its critical strain. This will be more prominent as the semiconductor chip gets thinner.
Another technique makes use of a push-up tool moving laterally across the vacuum platform to peel off a group of diced thin semiconductor devices from an adhesive tape. Such an apparatus is disclosed in U.S. Pat. No. 6,629,553 entitled “Method and System for Mounting Semiconductor Device, Semiconductor Device Separating System, and Method of Fabricating IC Card”. In this apparatus, peeling of the diced semiconductor devices is propagated by the lateral motion of a push-up tool that is raised to an appropriate height against a non-adhesive back surface of the adhesive tape, and moved across the said back surface to delaminate a row of semiconductor devices before being lowered again.
In this chip detachment process, the push-up tool is an object with a curved surface. It is mounted on a movable assembly and the object is moved laterally across a width of the whole wafer by a motorized table. After raising the object at one end of the wafer, when the object reaches an opposite end of the wafer, it is lowered down to be ready for the next separation cycle. This configuration is not meant to be used in die attachment system which is adapted to separate and pick-and-place one singulated semiconductor chip at a time during the chip detachment process. Furthermore, the object is moved across a whole row of semiconductor chips at the same height. It does not take into account the fragility of thinner and larger chips which may require controlled movement both vertically and horizontally with respect to each chip for optimized peeling action without damaging the chip.
A similar process is discussed in U.S. Pat. No. 6,561,743 entitled “Pellet Picking Method and Pellet Picking Apparatus”. However, the approach disclosed in this patent makes use of a stage of given height in place of the aforesaid object. This stage is movable on top of a vacuum platform along a horizontal plane in one direction. The vacuum suction provided by the holes on the platform together with a step formed in the stage creates sufficient tension on the adhesive tape to peel it away from the diced chips.
These prior art systems described above drive the push-up tools either vertically upwards and downwards, or laterally along a horizontal plane. Chip detachment by using vertically-driven push up pin(s) may not be practicable for critical applications involving large (eg. widths greater than 10 mm) and thin (eg. thickness less than 50 microns) semiconductor chips. On the other hand, if the driving mechanism provides only lateral motion for the push-up tool, it may not be easy to optimize the operating window for a given push-up tool in the detachment of large and thin semiconductor chips.
It is thus desirable to develop a driving mechanism that is operable to move a push-up tool in a combination of vertical and horizontal motions to assist in the delamination of each chip, especially for delaminating large and thin chips. It is also desirable that the driving mechanism is programmable in order to add versatility for adjusting for different operational requirements.